WooCommerce - Add a checkbox to the checkout, order emails and order meta

gistfile1.php

/**
 * Add the field to the checkout
 **/
add_action('woocommerce_after_order_notes', 'my_custom_checkout_field');

function my_custom_checkout_field( $checkout ) {
	
	echo '<div id="my_custom_checkout_field"><h3>'.__('My Field').'</h3>';
	woocommerce_form_field( 'my_field_name', array( 
		'type' 			=> 'checkbox', 
		'class' 		=> array('my-field-class form-row-wide'), 
		'label' 		=> __('Fill in this field'), 
		'placeholder' 	=> __('Enter a number'),
		), $checkout->get_value( 'my_field_name' ));
	
	echo '</div>';
}

/**
 * Update the order meta with field value
 **/
add_action('woocommerce_checkout_update_order_meta', 'my_custom_checkout_field_update_order_meta');

function my_custom_checkout_field_update_order_meta( $order_id ) {
	if ($_POST['my_field_name']) update_post_meta( $order_id, 'My Field', esc_attr($_POST['my_field_name']));
}

/**
 * Add the field to order emails
 **/
add_filter('woocommerce_email_order_meta_keys', 'my_custom_checkout_field_order_meta_keys');

function my_custom_checkout_field_order_meta_keys( $keys ) {
	$keys[] = 'My Field';
	return $keys;
}